[dyaroshev]

Our answer to this - is dynamic dispatch. If you want to have multiple version of the same kernel compiled - compile multiple dlls.

The big problem here is: ODR violations. We really didn't want to do the xsimd thing of forcing the user to pass an arch everywhere.

Also that kinda defeats the purpose of "simd portability" - any code with avx2 can't work for an arm platform.

eve just works everywhere.

Example: https://godbolt.org/z/bEGd7Tnb3

[janwas]

It is possible to avoid ODR violations :) We put the per-target code into unique namespaces, and export a function pointer to them.

[dyaroshev]

You can do many thing with macros and inline namespaces but I believe they run into problems when modules come into play. Can you compile the same code twice, with different flags with modules?

[janwas]

We use pragma target instead of compiler flags :)

[dyaroshev]

I don't think we understand each other.

We want to take one function and compile it twice:

``` namespace MEGA_MACRO {

void foo(std::span<int> s) { super_awesome_platform_specific_thing(s); }

} // namespace MEGA_MACRO ```

Whatever you do - the code above has to be written once but compiled twice. In one file/in many files - doesn't matter.

My point is - I don't think you can compile that code twice if you support modules.

[janwas]

I think I do understand, this is exactly what we do. (MEGA_MACRO == HWY_NAMESPACE)

Then we have a table of function pointers to &AVX2::foo, &AVX3::foo etc. As long as the module exports one single thing, which either calls into or exports this table, I do not see how it is incompatible with building your project using modules enabled?

(The way we compile the code twice is to re-include our source file, taking care that only the SIMD parts are actually seen by the compiler, and stuff like the module exports would only be compiled once.)

[dyaroshev]

> is to re-include our source file

Yeah - that means your source file is never a module. We would really like eve to be modularized, the CI times are unbearable.

I'd love to be proven wrong here, that'd be amazing. But I don't think google highway can be modularized.